This invention relates to lockdown mechanisms for completion components in hydrocarbon wells. For simplicity, much of the following discussion refers to tubing hanger lockdown mechanisms, although the invention is of more general applicability.
Tubing hangers and other completion components have a requirement to be rigidly locked into the wellhead, horizontal christmas tree or other receptacle in which they are landed, to ensure safe operating conditions. The tubing hanger is typically provided with an integral lock mechanism which when activated secures the tubing hanger to the wellhead. Any subsequent pressure load below the hanger will then not cause the hanger to rise within the wellbore, which would result in unsafe operating conditions.
Many tubing hanger lock mechanisms utilize an activating mandrel with a 4 degree taper to take account of equipment stack up tolerances. Activating mandrels with 4 degree tapers (or larger) are prone to work loose under certain operating conditions (e.g., vibration, cyclic loading, slug flow, etc.). This can lead to a reduction of the lock mechanism retention capacity, causing an unsafe condition.
Existing methods of retaining the mandrel in the set condition rely on either manual intervention with additional back up equipment (e.g., lockdown bolts in surface equipment), or integral devices that rely on friction contact with the activating mandrel.
The present invention provides a completion component having a lockdown mechanism comprising:
an actuating mandrel provided with a taper surface;
a locking dog engageable with the taper surface for movement between contracted and expanded positions;
a locking member carried by the actuating mandrel or completion component and having a radially directed locking profile;
a radially directed complementary locking profile being provided on the completion component or actuating mandrel, the locking profile being radially biased into engagement with the complementary locking profile so as to restrain the actuating mandrel against axial movement relative to the completion component; and
a running tool latch mechanism engageable with the locking member during installation of the completion component so as to move the locking profile and complementary locking profile out of engagement against said bias, whereby the actuating mandrel is free to move axially of the completion component.
Thus the invention provides a completion component lockdown mechanism with an actuating mandrel that includes a positively acting anti-backout device, which can be remotely deployed.
Preferably the locking profile and complementary locking profile comprise teeth having a positive rake angle such that forces acting on the actuating mandrel in a direction tending to move the locking dog towards the contracted position also cause the locking profile and complementary locking profile to move into tighter engagement.
The locking profile and/or the complementary locking profile may comprise an axially spaced series of teeth, to accommodate completion component stackup tolerances.
The lockdown mechanism may comprise a pin having a first end engageable by a latch piston of the running tool latch mechanism, and a second end arranged to move the locking member against said radial bias when the first end is so engaged. The pin first end may comprise a ball bearing.
The locking member may be a split ring which, for example, is radially inwardly biased and is carried in a groove formed in an axial bore of the actuating mandrel.
Further preferred features of the invention are in the following description of an illustrative embodiment.